Hydraulic gear-type machine of controllable displacement



Dec. 18, 1962 G. WIGGERMANN HYDRAULIC GEAR-TYPE MACHINE OF CONTROLLABLE DISPLACEMENT 3 SheetsSheet 1 Filed Sept. 22, 1960 In! ill Dec. 18, 1962 G. WIGGERMANN 3,

HYDRAULIC GEAR-TYPE MACHINE OF CONTROLLABLE DISPLACEMENT 3 Sheets-Sheet 2 Filed Sept. 22, 1960 Dec. 1962 e. WIGGERMANN HYDRAULIC GEAR-TYPE MACHINE 0F CONTROLLABLE DISPLACEMENT Filed Sept. 22, 1960 3 Sheets-Sheet 5 FIG.3

United States Patent 3,668,803 HYDRAULIC GEAR-TYPE MACHINE 0F CDNTROLLABLE DISPLACEMENT Georg Wiggermann, Kressbronn, Germany, assignor to Reiners & Wiggermann Getriebeund Maschinenbau, Kressbronn am Bodensee, Germany, a corporation of Germany Filed Sept. 22, 1960, Ser. No. 57,797 Claims priority, application Germany Sept. 23, 1959 6 Claims. (Cl. 103-120) My invention relates to hydraulic positive-displacement machines and in a more particular aspect to rotary hydraulic pumps of the type having a train of spur gears mounted in a liquid-containing housing and so journalled that the axial spacing of both outer gears from the intermediate gear can be varied continuously within a given range so that an increase in spacing between one gear pair is constrainedly accompanied by a reduction in axial spacing in the other gear pair and vice versa, thereby continuously varying the delivering quantity of the pump.

The objects, features and advantages of my invention, described hereinafter, will be more readily understood with reference to the accompanying drawing illustrating, by way of example, an embodiment of a gear-type hydraulic machine according to the invention. More specifically:

FIG. 1 shows schematically the machine in a somewhat exploded manner.

FIG/2 illustrates a modification of such a machine in the same manner.

.FIGQ3 is a sectional view through the machine of FIG. 2, the section being taken in a plane common to the axes of all appertaining spur gears; and

FIG. 4 is a lateral view onto part of the same machine, the viewing plane being indicated in FIG. 3 by the vertical line lV-IV.

Referring first, for explanatory purposes, to FIGS. 3

and 4, it will be recognized that in a hydraulic machine of this type three spur gears 2, 3 and 4 with involute gear teeth form a continuous train within a housing 1 which closely surrounds the two outer gears 2, 4 but leaves enough clearance laterally of the central gear 3 to form two chambers which, being under suction or compression during the operation of the machine, communicate with ducts 28 and 29 for connection of the machine to hydraulic lines. The shafts 5 and 24 of the respective outer gears 2 and 4 have fixed axes relative to the machine housing 1, whereas the central gear 3 is rotatably seated on an eccentric 21 on a shaft 6 so that turning of shaft 6 causes the rotation of axis of the central gear 3 to be shifted upwardly or downwardly along the geometric connecting line between the respective axes of the outer gears 2 and 4. Controllable displacement machines of this type are more fully described and explained in my copending application Serial No. 701,764, filed December 10, 1957 for Controllable Hydraulic Gear-Type Machine.

When a triple-gear machine of the above-mentioned type is so set that the axial spacing d and d of the respective outer gears from the central gear are equal, the machine, hereinafter referred to as a pump, has the quantitative delivery zero (V When the axial spacings are made progressively unequal by changing the eccentricity of the central-gear axis, the delivery increases, and its maximum (-V is reached when one outer gear has the maximum spacing and simultaneously the other outer the gear pair having the greater spacing of their axesmove from the suction chamber to the pressure chamber of the pump housing. Hence, when the adjustment is so made as to inverse the ratio of spacings of axes, the suction and pressure side become exchanged and the delivering direction is reversed.

By virtue of the fact that a controllable gear pump of the type described can be continuously controlled as to quantitative delivery as well as to delivering direction,

such pumps ought to have ideal operating properties and many possibilities of technological application. In fact, however, there are side effects which are extremely detrimental to the reversibility of the pump. If, for example,

a given direction of gear rotation is designated as positive, an investigation of the hydrostatic conditions reveals that the delivering pressure obtaining on the pressure side of the pump produces at the outer gear having the smaller;

axial spacing from the central gear a hydrostatic driving moment which, together with the driving moment occurring at the central gear, forms a sum torque opposed to the obtaining direction of rotation and hence acting negatively, whereas a positively acting hydrostatic driving moment always occurs at the outer gear having the greater spacing of axes.

The contact between the flanks of the gear piece at the two points of meshing engagement, aside from transr'nitting the driving motion, has the likewise important'purpose of sealing the pressure space from the suction spaceof the pump. As long as the meshing engagement" is loaded by the drive, the desired sealing actionis secured'.'---

This is the case for example at the outer gear having the smaller axial spacing and also at the central gear, because the sum of their hydrostatic driving moments act in opposition to the driving torque. In contrast thereto, the positive hydrostatic driving moment occurring at the outer gear having the greater spacing of axes has a very detrimental etlect upon the scaling function because this moment, at a given magnitude of delivering pressure, he

comes capable of overcoming the negative friction resistances of this outer gear so as to independently drive this outer gear. As a consequence, the previous normal flank engagement of the teeth at the central gear tends to become eliminated and each tooth tends to'change over to the opposite flank. Since in devices of this type, a relatively great amount of clearance between the gear teeth and hence between the pressure space and suction space is necessary, the just-mentioned phenomenon may produce a hydraulic short circuit between these two pump spaces with a sufliciently large flow cross section to cause a sudden drop in delivering pressure. The remaining.

slight delivering pressure is then insuflicient to overcome the frictional resistance of this outer gear so that the original sealing engagement in the meshing area with the central gear becomes re-established. The delivering pressure immediately rises and thus also the positive hydrostatic driving moment. Hence, the outer gear will again move more rapidly-than corresponds to the driving speed.

This again results in the above-described hydraulic short circuit, the resulting effect on delivering pressure, and so forth. This cycle of phenomena is repeated in a rapid sequence and can be avoided only if the pump is subjected to relaitvely low delivering pressure. The above-mentioned ideal properties of triple-gear controllable pumps, however, are rather limited in practice, if such pumps for the foregoing reasons are applicable only for small delivering pressures.

It is, therefore, an object of the invention to devise a triple-gear pump of the controllable type which is capable of operating at least in one, preferably in both, directions of delivery, with the desired pressure limited only by the supporting strength of the bearings and the strength of the pump housing.

To this 'end, and in accordance with a feature of my invention, I connect-the pump drive shaft to one of the two outer gears and I further limit the adjusting range ofthe radial spacings between the axes of the respective outer gears and the central gear so'that the radial spacing of the driving outer gear is always greater or at least equal to the radial spacing of the other outer gear from the central; gear axis.

By'virtue of the requirement that the driving torque be applied to the one outer gear having the greater axial spacing, this outer gear is the one that receives from the delivering pressure a positive hydrostatic driving moment. However, since from this particular outer gear the driving moment is derived which is applied to the hydrostatically negative driven central gear and the remaining, free outer gear,- only negative peripheral forces can act in the meshingiregion of the positivelydriven outer gear and the central gear, sothat the meshing engagement of the toothed flanks in thisregion can never become disengaged, and the positive hydraulic driving moment occurring in the originally driven outer gear itself is always smaller than ,the total driving-momentof the pump and hence cannot. have any detrimental effect with respect to pressure sealing conditions. Consequently, with such a design and operation of the triple-gear pum a continuously controllable deliveryzfrom V to V is attained for any desired delivering pressure with a'uniform direction of. rotation, although only in one direction of delivery. This sufiices to render such a pump .suitabel for satisfactory, performance in manycasesof application.

.Anotherobject ofmy invention is to devise a controllable-deliverypump of the type described above so as togpermita continuousicontrol and regulation of delivery in both direct'ionsatthe desired "high pressure.

.For this purpose, and in accordance withanother'featureofmydnvention, l'combine two delivery-controllable tfiple-gearpumpswhos'erespective control devices permit a variation .in axial spacing in both directions from the v condition, the combination being such that both pumps are connectedin. mechanical parallel relation'with'respect tosthe mechanicali drive, but are connected in series in hydraulic; respects. 'Ihedelivery. control members of the two combined pumps are mechanicallycoupled with each otherisothatat zero delivery of the combination the respectiveoutergearsin each component pump possess equal axial spacingsfrom the appertaining central gear, whereas 7 the-actuation of a'control member common to'both component pumps causesthe individual pumps to become adjusted 'sothat the-originally'driven outergears are simultaneously changed in-mutually opposed sense with respect to their:- spacing .fromitheiappertaining central. gear.

The above-described combinationiof two triple-gear pumps according to theinvention is predicated upon the conceptthat each individual pump in this combination can be made: toaoperate' in only one direction of. delivery. That is, in a machine according to the invention, one componentpump isiactivealways in one direction, and the other component only in the other direction of delivery.

Due'to the 'factthat'in-theone particular pump which is not'active' at 'a tirne, the axialspacingof the driving outer gear-fromi-the central gearis smaller than the axial spac- 4 ing of the other outer gear, this pump always permits the flow delivered from the other pump to pass through without appreciable resistance.

Further features according to my invention relate to a number of structural details. According to one of these further features, the combination of two triple-gear controllable-delivery pumps can be composed of two individually complete and operative pump units whose respective two driving outer gears are mechanically connected with each other, and whose delivery-control devices are likewise coupled with each other. According to another feature of the invention, however, a considerable simplification and a less costly design is achieved by accommodating the two trains of triple gears within a single closed. three-part housing and to fasten the two driving outer gears of the respective component pump units on a common drive shaft. The respective control members of the two pump units, designed for example as eccentric shafts and acting upon the two central gears, are then preferably mounted within the common housing and are mechanically coupled with each other and provided with a common control shaft which extend to the outside of-the housing. By virtue of such a common housing'the apparatus can be given minimized overall dimensions, minimized manufacturing costs and a particularly reliable performance.

As mentioned above, the coupling of the two delivery control members of the two component pumps, for example the eccentric shafts upon which the respective central gears are journalled, must be of such character that the two central gears, during each change incontrol setting, are displaced in mutually opposed directions relative to the respective driving outergears." According to one of the more specific features of my invention, this purpose The same functioning, according .toranoth'er feature of my invention, is obtained by'arranging'the'two'eccentric shafts for displacing therespective two central gears, aligned on a common axis and providingbetweenthe two eccentric shafts 'a-reversing' gearing of suitable typje, for example a train of bevel gears, so that .the two. eccentric shafts are always displaced'thesame angular amounts, but in'mutually opposed" directions from the zero-delivery position;

According to still another featuresoffmy invention, the

hydraulic connection for passing'the hydraulic medium from one to the other. pump is provided'with a suction.

valve whose suction side'communicates with the sump or other storage container for the medium to be deliv ered. When the twin-type triple-gear pump according to the invention operates in a closed circulation for'the hydraulic medium, each branchofth'e circulatory'conduit system must beprovided with a pressure-responsive valve 7 and with a-suction-responsive valve. The 'former valve is required for limiting the'maximum pressure in'both directions ofdelivery, whereasthe ,suction'valve is desirable for compensating from the storage'container any leakage-oil losses occurring in the hydraulic components of the system, for example in the oil-driven hydraulic motors, cylinders, pistons etc. According to the feature of my invention last'mentioned, the two suction valves are substituted by a single'suction valve, thus securing'a desirable simplification and reduction pump and the accessory plant.

The foregoing and more specific objects, advantages and features 'of' my invention, said features being set forth in particularityin the-claimsannexed hereto, will in cost of the be apparent from, and will be mentioned in, the following description of the embodiments illustrated on the accompanying drawings.

According to FIG. 1, two pump housings 1, 1' are each provided with a train of three spur gears 2, 3, 4 and 2, 3, 4, respectively. The outer gears 2, 2' are firmly joined with a common drive shaft 5. The intermediate or central gears 3, 3' are journalled on respective shafts 6, 6 so that their respective axes of rotation are eccentrically related to the axes of the shafts 6, 6'. Consequently, a rotary displacement of shafts 6 and 6 causes the eccentric axes of the central gears 3, 3 to be shifted from one toward the other outer gear. The remaining, free outer gears 4, 4' have their respective shafts 24, 24' journalled in the pump housings 1, 1' so that the shaft axes are fixed relative to these housings.

The pump may be driven from a motor (not shown) by means of a coupling 7, for example in the clockwise direction indicated in FIG. 1 by the arrow A. The two shafts 6, 6 are provided with respective cranks 8, 8' which are located between the two housings 1, 1' and are connected with each other by a connecting rod 9. A control lever 10 is rigidly mounted on shaft 6 and can be shifted over a given angular range preferably limited by respective stops S and S Any angular displacement of control arm 10 and of the connected shaft 6 is transmitted by the crank and linking rod mechanism 8, 9, 8' to the shaft 6' so as to always move the shaft 6 in the same sense and by the same angle as the shaft 6.

The eccentric journals 11 and 11' are illustrated schematically in FIGS. 1 and 2 as cranks for simplification of the illustration, but are actually designed as eccentric shaft portions as shown at 21 in FIGS. 3 and 4. Due to the mutually parallel displacement between the two control shafts 6 and 6 on the two sides respectively of the respective vertical center axis Z, and a proper arrangement of these eccentric journals 11, 11, or shaft portions 21), any positional change of the control arm 10 starting from any dash-dot middle position V toward the limit position +V (the latter position being shown in FIG. 1 by a solid line) causes the eccentric 11 to shift the center gear 3 upwardly and simultaneously causes the eccentric 11' to shift the center gear 3' downwardly. When the control arm 10 is moved from the V position toward the V. position, the eccentric 11 shifts the central gear 3 downwardly while the eccentric 11 shifts the gear 3' upwardly.

The two trains of triple gears are so enclosed by the housing portions 1 and 1 that a hollow space remains between the housing wall and each side of the central gear 3 or 3. Two corresponding chambers 26 and 26' (FIG. 1) thus formed in the respective pump housings communicate with conduits, ducts or other lines 12, 12', (FIG. 2) through duct 28 (FIG. 4). The two other chambers 27 and 27' are connected with each other by a connecting conduit, channel or line 13 into which the fluid flows through duct 29. The lines 12, 13, 12' form part of the hydraulic circulatory system suitable, for example, for driving a hydraulic actuator under control by the illustrated twin-type pump. Connected to the line 13 is a suction valve 14 whose suction duct 15 com'muni cates with the oil content of a storage container or sump 16.

The above-described pump operates as follows:

As mentioned, the pump forms part of a hydraulic circulatory system such as used for operating a hydraulic actuator which may consist of a piston displaceable in a cylinder (not shown). The medium coming from the actuator, such as the cylinder, passes through the line 12 and enters through inlet 28 into the suction chamber 26 of the component pump P oil is delivered to chamber 27' and through the connecting line 13. While thus passing from chamber 26' to 27', the medium cannot develop any appreciable delivering pressure because such pressure, occurring in the From this chamber, the

chamber 27' would impose a hydraulic driving torque upon the free outer gear 4' and would cause its gear tooth flanks to become disengaged from those of the central gear 3'.

The second component pump P sucks the medium from the connecting line 13 and impels it from chamber 27 to chamber 26 and into the line 12, while overcoming the counter-pressure in chamber 26. If, due to leakageoil losses or elastic displacement, the quantity of medium flowing to the pump P is smaller than the volumetric delivery of the pump P a negative pressure occurs in the connecting line 13 which has the effect that additional hydraulic medium is inducted from the storage container 16 through the suction valve 14, thus maintaining the entire hydraulic system always in completely filled condition.

When the control arm 10 is placed in its mid-position V (shown in FIG. lby a dot-and-dash line), the positions of the respective eccentrics 11 and 11 are such that the central gears 3 and 3' are accurately located midway between the appertaining outer gears 2 and 4, or 2' and 4'. With this setting, the delivery of the twin pump is zero. When the control arm 10 is displaced from V toward the position V the central gears 3, 3' become progressively displaced so that now the central gear 3 approaches the driving outer gear 2, whereas the central gear 3' moves away from the driving outer gear 2. Consequently, when the control arm 10 is shifted from one position through the zero position V to the other side of its control range, the delivering direction of the twin pump is reversed, the pump P becomes active whereas the pump P now permits the pumps are always the same for a given amount of displacement of arm 19 from the V position.

The modified embodiment illustrated in FIGS. 2, 3 and 4 is in accordance with the one described above with reference to FIG. 1, with the exception of the arrangernent of the control shafts 6 and 6 and the coupling between these two shafts. The same reference char acters are used in all illustrations for respectively similar elements. The combination of the two component pumps according to FIGS. 2, 3 and 4 is also identical with the one described-above, so that the following description of the modified embodiment may be limited to those features that differ from the pump previously described.

As apparent from FIGS. 2 and 3, the two control shafts 6 and 6' of the second embodiment are axially aligned with each other and are both located on one and the same side of the center plane defined by the two vertical center axes denoted by Z of the component pumps (FIG.2). These two aligned shafts 6, 6' are coupled in this embodiment by a reversing gearing which comprises three bevel gears 17, 18, 17, of which gears 17, 17' are fastened to respective shafts 6 and 6, the intermediate bevel gear 18 being rotatable on a shaft 25 which is fixedly mounted in a portion 1a of the pump parent from FIGS. 3 and 4 where one of them is denoted by 21.

In FIG. 2, the control arm 10 is shown in the -V position. When the control arm is moved from the left" toward the right, it will approach the V position. During such displacement, the eccentric 11 (21 in FIG. 3)

shifts the central gear 3 upwardly, whereas theeccentric 11' shifts the central gear 3' downwardly. When the control member. 1! reaches the V position, the spacing of both outer gears from the central gear 3, 3" in each component pump are equalto each other. A further angular displacement of the control member 10 toward the right has theeffect of moving the central gear 3 from its mid-position downwardly. Then the delivering direction isreversed. In the negativecontrol range, with the pump shaft being driven clockwise as indicated by the arrow- A'in FIG. 2, the pump P impels the hydraulic medium iVhiCh arrives in line 12 and passes through the inactive pump P and theconnecting line 13, into the line 12'. Conversely, in the positive control range of 'member .10, the pump P is active upon the hydraulic medium which is supplied through line 12 and passes through the then inactive component pump P and the connecting line 13 so as to issue under pressure to'the line 12.

It will be'noted that in both, the embodiments of FIG. 1 and FIG. 2 described above, only a single control member, namely the member 10, need be actuated for affording a stepless change in delivering quantity in both directions of delivery. For each delivering direction, one of the respective pumps is active and thus exhibits the advantageous properties mentioned in the introductory portion or this specification. Consequently, the twin triple-gear pump according tothe invention satisfies all requirements for a satisfactory performance in both directions of operation.

.As shownin FIG. 3, thetwo gear trains are preferably accommodated Within a single housing. This housing is shown composed of portions 1, 1 and 1a which are firmly joined together by fastening bolts passing through such openings as the one denoted by 30' in FIG. 4.

Adelivery-controllab le and reversible triple-gear pump 'of the twin-type according .to the invention constitutes anovel hydraulic apparatus which possessesbut a single displaceablezcontrol member whose actuation affords the reliable performance of any desired hydraulic control and actuation in hydraulically operating drive systems. The.

absenceof slide valves, rotary valves, or other movable displacing components other than the gears themselves,

resultsinproVidingan. extremely rugged pump of im-- proved'reliability as desirable in many hydraulic drives such asused for various machine tools and'other fabrieatingv and :processing machinery.

It-Will be'obvious tothose skilled'in the art, upon a-studyof thisdisclosure, that the invention is-not'limited to the particular embodiments illustrated and described herein, but can be modified in various respects'without departing from the .essentialyfeatures of my invention'and withinathe scope of the claims annexed hereto; It is also obvious that machines according" to the invention aresuitablenot only as'pumps, but can likewise-be usedas controllableand reversible hydraulic motors. Thus, the actuator to be connected to the lines 12 and 12', according to'FIGS. l or 2, may consist of a machine identical with the one according to'the invention.

1 claim:

1. Ahydraulic positive displacement machine, comprising ,a housing having inlet and outlet ducts, a plurality of :gears having involute teeth: on their outer periphery and comprising an intermediate gear and two outer gears all mounted forrotationin said housing, said outer gears beingmesha-ble with said intermediate gear to forrn'a gear train, at least twoof said gears forming pressure and suction chambers together with said housing, a drive shaft connected with one of said outer gearsfor driving same, and control means for varying the respective radial spacing between the axes of the two outer gears and said intermediate gear in such manner and within a predetermined adjustin'grange such that the radial spacing between the axes of said one outer gear and said intermediate gear is'always limited to at least the radial spacing between the axes of said other outer gear and said intermediate gear, and so that an increase in radial spacing between said intermediate gear and said one outer gear is always accompanied by v.a reduction in radial spacing between said intermediate gear and-said other outer gear, whereby a change insaid. radial spacing causes a continuous variation of the delivery quantity of displacement andpermits-a selective change of the flow direction through said chambers.

2. A controllable-delivery pumping unit, comprising a housing, a pair of triple-gear component pumps mounted within said housing, said component pumps each having three gears meshableto. form a gear train and located so that their axes of rotation lie approximately in a com mon plane, at least two of the gears of each componentpumps forming pressure and suction chambers together'with said housing, a drive shaft connected in parallel with one outer gear of the respective gear train of eachof said component pumps, each of said component pumpsbeing provided with a control device selectively variable from a zero delivery position in either of two opposed delivery directions for changing the radial spacing of the outer gears of the respective gear train from the intermediate .gear thereof, duct means hydraulically connecting the respective chambers of each of said component pumps in series, means interconnecting said control devices 'solhat the two outer gears in'each of said component pumps have their respective axes spaced an equal distance from the axis of the respective intermediate gear of the respective gear train when therespective control devicesare both set at zero delivery position and sothat movement of said control devices from their zero delivery position .causes the two outer gears in the respective component pumps which are connected in parallel withsaid drive shaft to move relative to the intermediate gears in their gear. trains in respectively opposite directions.

3. A controllable-delivery pumping unit according to claimz2, said housing comprising three portions fixedly assembled together to accommodate said two component pumps, said drive shaft forming a common shaft connected with each of said one outer gears, said control devices comprising eccentric shafts forming rotational axesv for the :respective intermediate gears, said control devices further including means operably connecting saidshaft connected to the a control shaft connectedto the eccentric shaftof one ofsaid' intermediate gears and extending to the outside of said housing, and lever means connected to saidicontrol shaft'for controlling the flow invboth saidzcomponentpumps of said unit.

:4; A controllable-delivery pumping unit according to claim 3, said eccentric shafts both being mounted'in said housing, said meansconnecting the eccentric shafts together comprising a parallel-motion'crank mechanism disposed in said housing'for constraining displacement ofsaid eccentric shafts so that said two eccentric shafts always rotate in the same sense of rotation and by the same-angular amounts.

"5. A controllable-delivery pumping unit according to claim 3, said'eccentric shaftsi-being journalled in mutual coaxial alignment with said'housing, said means connecting, the eccentricshafts together comprising a bevel gearing operably connected so thatthe twoveccentric shafts rotate in mutually opposite directions and are always displaced relative to. each other, counting'from said zero delivery position. of said control device, by the same angle and in said mutually opposed directions.

eccentric shafts'together, a control eccentric. shafts together,

6.'A continuous-delivery pumping unit according to- 1 suction valve-having a suction side communicating with said storage containerxfor inducting hydraulic fluid therefrom.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Frelin Mar. 21, 1933 Grosser Dec. 28, 1948 Muller Oct. 24, 1950 Rorive Apr. 17, 1951 Bergsma Mar. 18, 1952 Kumpf et a1 Feb. 2, 1954 FOREIGN PATENTS Switzerland Dec. 16, 1925 Germany Nov. 10, 1925 Great Britain Jan. 11, 1956 Germany Sept. 15, 1952 France May 19, 1959 

